The present invention relates to an air data system. More particularly, the present invention relates to a system for preventing and removing moisture ingested (from both condensation and liquid ingestion) into an air data sensor system which is used on, for example, air vehicles and weather monitoring sites.
Air data sensing probes are typically embodied in sensing systems such as Pitot tubes, Pitot-static tubes, flush static ports, and multi-functional probes. The sensing probes typically measure static flow angle or Pitot pressure. The sensors provide a pneumatic input, such as air pressure, to a transducer which converts the pneumatic input to an electrical output indicative of the pneumatic input. Such probes are typically electrically heated for de-icing and anti-icing.
During ground or flight operations, the aircraft, and consequently the probe, is subjected to conditions such as rain, sleet, snow, ice, high pressure washing sprays, temperature and humidity extremes. During such operations, moisture can be ingested into the probe. Thus, moisture ingestion has been a long standing problem with such probes.
Further, during the ascent of an aircraft, an air pressure differential is created between the interior of the probe and the exterior air mass. The air pressure is higher inside the probe until the pressure bleeds off and equalizes with the exterior air mass. The opposite is true during descents. The air pressure inside the probe is lower than the external air mass until equilibrium occurs. The volume and rate of this "bleeding" in the system is a function of the total air volume of the system, and the rate of climb or descent of the aircraft. Once moisture is ingested into the system, the bleeding can force the moisture well into the pneumatic passageways in the system. If cold temperatures are then encountered, the moisture freezes thereby blocking the pneumatic passageways causing erroneous air data readings.
Another problem with moisture ingestion has also been observed. During ground operations, the probe is typically powered up and heated to remove any accumulated moisture. Warm air can carry a high amount of water vapor into the probe. Heating of the air in the probe increases the water carrying capacity of the air and may force water vapor upstream and downstream in the pneumatic lines. Furthermore, meniscuses formed in the relatively small diameter pneumatic tubes may be undesirably forced downstream toward the transducer. Water vapor carried into the system typically condenses at the cool points of the probe (i.e., at temperatures below the dew point temperature of the water vapor). If the probe is exposed to cold enough temperatures, the condensed water can freeze thereby blocking the pneumatic tubes in the probe, again causing erroneous pressure readings.
Prior systems for dealing with moisture which is ingested into air data probes included moisture traps or bottles. While such traps or bottles reflect important advances in the art, maintenance is required during ground operations to open or empty the traps or bottles to eliminate water from the system. Thus, there is a continuing need for systems which eliminate moisture, in the form of water, ice or vapor, from air data probes and which require no maintenance during ground operations.